Genetic disorders caused by absence of or a defect in a desirable gene (loss of function) or expression of an undesirable or defective gene (gain of function) lead to a variety of diseases. At present, adeno-associated virus (AAV) vectors are recognized as the gene transfer vectors of choice for therapeutic applications since they have the best safety and efficacy profile for the delivery of genes in vivo. Of the AAV serotypes isolated so far, AAV2 and AAV8 have been used to target the liver of humans affected by severe hemophilia B. Both vectors worked efficiently and, in the case of AAV8, long-term expression of the therapeutic transgene was documented. Recent data from humans showed that targeting the liver with an AAV vector achieves long-term expression of the FIX transgene at therapeutic levels. Additionally, several Phase 1 and Phase 2 clinical trials using AAV serotypes 1, 2 and chimeric 2.5 have been reported for the treatment of Duchenne muscular dystrophy (DMD) and alpha-1 antitrypsin deficiency (D. E. Bowles, S. W J McPhee, C. Li, S. J. Gray, J. J. Samulski, A. S. Camp, J. Li, B. Wang, P. E. Monahan, J. E. Rabinowitz, J. C. Grieger, La. Govindasamy, M. Agbandje-McKenna, X Xiao and R. J. Samulski, Molecular Therapy, 20, 443-455 (2012); M. L. Brantly, J. D. Chulay, L. Wang, C. Mueller, M. Humphries, L. T. Spencer, F. Rouhani, T. J. Conlon, R. Calcedo, M. R. Betts, C. Spencer, B. J. Byrne, J. M. Wilson, T. R. Flotte, Sustained transgene expression despite T lymphocyte responses in a clinical trial of rAAV1-AAT gene therapy. Proceedings of the National Academy of Sciences of the United States of America 106, 16363-16368 (2009); T. R. Flotte, M. L. Brantly, L. T. Spencer, B. J. Byrne, C. T. Spencer, D. J. Baker, M. Humphries, Phase I trial of intramuscular injection of a recombinant adeno-associated virus alpha 1-antitrypsin (rAAV2-CB-hAAT) gene vector to AAT-deficient adults. Human gene therapy 15, 93-128 (2004); T. R. Flotte, B. C. Trapnell, M. Humphries, B. Carey, R. Calcedo, F. Rouhani, M. Campbell-Thompson, A. T. Yachnis, R. A. Sandhaus, N. G. McElvaney, C. Mueller, L. M. Messina, J. M. Wilson, M. Brantly, D. R. Knop, G. J. Ye, J. D. Chulay, Phase 2 clinical trial of a recombinant adeno-associated viral vector expressing alpha1-antitrypsin: interim results. Human gene therapy 22, 1239-1247 (2011); C. Mueller, J. D. Chulay, B. C. Trapnell, M. Humphries, B. Carey, R. A. Sandhaus, N. G. McElvaney, L. Messina, Q. Tang, F. N. Rouhani, M. Campbell-Thompson, A. D. Fu, A. Yachnis, D. R. Knop, G. J. Ye, M. Brantly, R. Calcedo, S. Somanathan, L. P. Richman, R. H. Vonderheide, M. A. Hulme, T. M. Brusko, J. M. Wilson, T. R. Flotte, Human Treg responses allow sustained recombinant adeno-associated virus-mediated transgene expression. The Journal of clinical investigation 123, 5310-5318 (2013)).
Adeno-associated virus (AAV), a member of the Parvovirus family, is a small nonenveloped, icosahedral virus with single-stranded linear DNA genomes of 4.7 kilobases (kb). AAV is assigned to the genus, Dependovirus, because the virus was discovered as a contaminant in purified adenovirus stocks (D. M. Knipe, P. M. Howley, Field's Virology, Lippincott Williams & Wilkins, Philadelphia, ed. Sixth, 2013). In its wild-type state, AAV depends on a helper virus—typically adenovirus—to provide necessary protein factors for replication, as AAV is naturally replication-defective. The 4.7-kb genome of AAV is flanked by two inverted terminal repeats (ITRs) that fold into a hairpin shape important for replication. Being naturally replication-defective and capable of transducing nearly every cell type in the human body, AAV represents an ideal vector for therapeutic use in gene therapy or vaccine delivery. In it's wild-type state, AAV's life cycle includes a latent phase during which AAV genomes, after infection, are site-specifically integrated into host chromosomes and an infectious phase during which, following either adenovirus or herpes simplex virus infection, the integrated genomes are subsequently rescued, replicated, and packaged into infectious viruses. When vectorized, the viral Rep and Cap genes of AAV are removed and provided in trans during virus production, making the ITRs the only viral DNA that remains (A. Vasileva, R. Jessberger, Nature reviews. Microbiology, 3, 837-847 (2005)). Rep and Cap are then replaced with an array of possible transfer vector configurations to perform gene addition or gene targeting. These vectorized recombinant AAVs (rAAV) transduce both dividing and non-dividing cells, and show robust stable expression in quiescent tissues like skeletal muscle. The number of rAAV gene therapy clinical trials that have been completed or are ongoing to treat various inherited or acquired diseases is increasing dramatically as rAAV-based therapies increase in popularity. Similarly, in the clinical vaccine space, there have been numerous recent preclinical studies and one ongoing clinical trial using rAAV as a vector to deliver antibody expression cassettes in passive vaccine approaches for human/simian immunodeficiency virus (HIV/SIV), influenza virus, henipavirus, and human papilloma virus (HPV). (See, P. R. Johnson, B. C. Schnepp, J. Zhang, M. J. Connell, S. M. Greene, E. Yuste, R. C. Desrosiers, K. R. Clark, Nature medicine 15, 901-906 (2009); A. B. Balazs, J. Chen, C. M. Hong, D. S. Rao, L. Yang, D. Baltimore, Nature 481, 81-84 (2012); A. B. Balazs, Y. Ouyang, C. M. Hong, J. Chen, S. M. Nguyen, D. S. Rao, D. S. An, D. Baltimore, Nature medicine 20, 296-300 (2014); A. B. Balazs, J. D. Bloom, C. M. Hong, D. S. Rao, D. Baltimore, Nature biotechnology 31, 647-652 (2013); M. P. Limberis, V. S. Adam, G. Wong, J. Gren, D. Kobasa, T. M. Ross, G. P. Kobinger, A. Tretiakova, J. M., Science translational medicine 5, 187ra172 (2013); M. P. Limberis, T. Racine, D. Kobasa, Y. Li, G. F. Gao, G. Kobinger, J. M. Wilson, Vectored expression of the broadly neutralizing antibody FI6 in mouse airway provides partial protection against a new avian influenza A virus, H7N9. Clinical and vaccine immunology: CVI 20, 1836-1837 (2013); J. Lin, R. Calcedo, L. H. Vandenberghe, P. Bell, S. Somanathan, J. M. Wilson, Journal of virology 83, 12738-12750 (2009); I. Sipo, M. Knauf, H. Fechner, W. Poller, O. Planz, R. Kurth, S. Norley, Vaccine 29, 1690-1699 (2011); A. Ploquin, J. Szecsi, C. Mathieu, V. Guillaume, V. Barateau, K. C. Ong, K. T. Wong, F. L. Cosset, B. Horvat, A. Salvetti, The Journal of infectious diseases 207, 469-478 (2013); D. Kuck, T. Lau, B. Leuchs, A. Kern, M. Muller, L. Gissmann, J. A. Kleinschmidt, Journal of virology 80, 2621-2630 (2006); K. Nieto, A. Kern, B. Leuchs, L. Gissmann, M. Muller, J. A. Kleinschmidt, Antiviral therapy 14, 1125-1137 (2009); K. Nieto, C. Stahl-Hennig, B. Leuchs, M. Muller, L. Gissmann, J. A. Kleinschmidt, Human gene therapy 23, 733-741 (2012); and L. Zhou, T. Zhu, X. Ye, L. Yang, B. Wang, X. Liang, L. Lu, Y. P. Tsao, S. L. Chen, J. Li, X. Xiao, Human gene therapy 21, 109-119 (2010).) The properties of non-pathogenicity, broad host range of infectivity, including non-dividing cells, and potential site-specific chromosomal integration make AAV an attractive tool for gene transfer.
The first rAAV-based gene therapy to be approved in the Western world (Glybera® for lipoprotein lipase deficiency, approved for use in 2012 in the European Union) has stimulated the gene therapy community, investors and regulators to the real possibility of moving rAAV therapies into the clinic globally. Yet, despite the impressive abilities of rAAV to transduce a variety of tissue and cell types, skeletal muscle has been historically been one of the most challenging tissues to transduce at high levels sufficient to provide therapeutic levels of expression of delivered transgene products. Indeed, the current best skeletal muscle tropic serotypes (rAAV 1, 2, 6 and 8) have seen limited success clinically for intramuscular delivery of transgene products in gene therapy trials for skeletal muscle disorders. This likely stems from the fact that preclinical modeling with rAAV to determine the best capsid serotypes for transducing target tissues is done in animal models—typically mice—which do not necessarily recapitulate the tissue and cell tropism each rAAV has in humans, nor the transduction capabilities at treatment.
The recent excitement surrounding the possible use of rAAV as a vector for delivery of vaccines providing passive immunoprotection against pathogenic viruses like HIV and influenza virus in particular, has renewed the urgency for rAAV capsids capable of highly efficient intramuscular delivery for this unique vaccination approach in humans. Given the limitations with efficient human skeletal muscle transduction with existing rAAV serotypes, we sought to bioengineer a clinical rAAV vector candidate that can efficiently transduce human skeletal muscle at a level sufficient to express therapeutic levels of broad-spectrum antibodies for vaccine strategies or genes essential for muscle disorder treatment.
A variety of published US applications describe AAV vectors and virions, including U.S. Publication Nos. 2015/0176027, 2015/0023924, 2014/0348794, 2014/0242031, and 2012/0164106; all of which are incorporated by reference herein in their entireties.
However, high levels of transduction are needed for muscle gene therapy trials as there are physical limitations to how much AAV can be delivered in a single intramuscular injection which is further complicated by the fact that injections need to span the length of the muscle to correct defects along the muscle length. If an AAV had superior human skeletal muscle transduction, a lower dose and fewer injections would be needed to achieve therapeutic relevance. Similarly for use as a vaccine delivery tool, high efficiency transduction and stability is needed to achieve robust secretion of antibodies encoded within the AAV to reach therapeutic levels of circulating antibodies in the blood.
There remains, therefore, a need in the art for AAV vectors with improved human skeletal muscle transduction. The present invention meets this need by providing variant AAV capsid polypeptides that demonstrate significantly improved human skeletal muscle transduction over existing capsid serotypes in humanized muscle mice in vivo, in numerous human muscle cell cultures in vitro, and most importantly in human skeletal muscle explants ex vivo. The present invention utilizes directed evolution by DNA gene shuffling to characterize and screen for such variant AAV capsid polypeptides that have high efficiency skeletal muscle transduction for human skeletal muscle specifically.